1. Field of the Invention
The present invention relates to the field of computer memories, and more particularly, to an improved single in-line dynamic random access memory (DRAM) module for storing and retrieving data in a computer system.
2. Art Background
Computer systems commonly utilize banks of dynamic random access memory (DRAM) for storing data and computer programs for a variety of tasks. For example, in a bit map computer display system, each pixel disposed on a cathode ray tube (CRT) display is assigned a single bit digital value to represent the pixel in memory, or a multiple bit digital value to represent color. Computers have traditionally addressed their memories in 8 bit, 16 bit, 32 bit, 64 bit or larger increments. Typically one memory cycle has the capability of transferring a predetermined number of bits. Over the years since the advent of digital computers, a variety of memory configurations and architectures have been developed to maximize the performance of data processing systems. As will be described, the present invention discloses an improved single in-line memory module containing a plurality of DRAMS for use in a digital computing system.
A number of computing systems, such as the engineering workstations manufactured by the assignee of the present application, Sun Microsystems, Inc., have provided dynamic RAM memory through the use of DRAM modules, which plug into the main printed circuit board ("mother board") of the workstation. These DRAM modules provide a known amount of memory per module, with predetermined cycle times and operating modes. For example, a DRAM module offered by the Toshiba Corporation provides 72 megabits, 36 megabits, and other combinations of RAM storage capacity, on printed circuit boards for insertion into memory expansion slots on computer mother boards. However, these prior art DRAM modules provide limited bandwidth for data transfer to and from the processor, and further lack many of the capabilities (such as error correction and control) desirable in modern computer systems.
As will be described, the present invention provides an improved single in-line DRAM memory module which may be used in conjunction with modern engineering workstations or other digital computers. The present invention utilizes unique cross bar switches (CBS) for the multiplexing and pipelining of data. Moreover, the present invention permits the memory controller to conduct error detection and recovery on data stored within the DRAMS.